"Cinematic" is a descriptor often assigned to instrumental bands, a catchall term that frequently serves as a polite way of saying "background music." Although On Fillmore creates sparse, mysterious sonic landscapes that occasionally function as film scores, the duo of Darin Gray and Glenn Kotche hates background music. Eschewing traditional structures, the band lulls, intrigues, startles and grinds, while crafting works with an illustrative quality. Some instrumental music feels like a soundtrack searching for a film, but Gray and Kotche create songs that invent their own images.

"What we're hoping to do is create actual places with our music," says Gray of Extended Vacation, On Fillmore's fourth full-length. "The catch is that they're not specific places, which is what makes it hard to do." These topographical motivations come through exactly 77 seconds into the album's opener, "Checking In," when assertive upright bass, diving-board percussion and an orchestral ensemble of bird noises rudely awakens a dreamy vibraphone intro. It's an aural wormhole delivering the listener to a destination that exists somewhere between a tropical rainforest and a musty, punk-rock basement venue.

Conceptuality aside, the title Extended Vacation bears a literal significance for On Fillmore. The duo rarely plays together or even sees each other because of geography — Gray lives in Edwardsville, Illinois, Kotche in Chicago — and demanding schedules: The former is a dedicated father with a full-time job, and the latter plays drums in Wilco. "Glenn's schedule is nuts," says Gray. "It doesn't allow us a lot of time to work. But with that said, it's also given us a lot of opportunities we would never have otherwise."

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One such perk was the opportunity to record Vacation at the Loft, the Chicago practice space and studio where Wilco crafted its Yankee Hotel Foxtrot album and subsequently served as the setting for the tumultuous documentary I Am Trying to Break Your Heart. (Kotche recalls his introduction to the Loft like this: "The first day of shooting that movie was my first day in Wilco. It was fairly overwhelming.") Fittingly, Kotche's relationship with Darin Gray was borne of a similar trial-by-fire experience during recording sessions for mutual friend Jim O'Rourke's bizarro-pop opus, Eureka.

"We literally met in the studio and were recording together an hour and a half later," Gray says. "It was one of those immediate connections. We could instantly play together, and from that day we basically became best friends." The respect is more than mutual. "I had seen Darin perform a few times before the Eureka sessions and was just blown away," Kotche says. "He's an unsung hero. I think he's the most underrated, under-appreciated musician on the planet. Period."

O'Rourke and Gray had worked together in advance of Eureka in the Chicago-based '90s group Brise-Glace, as well as other projects such as Gastr del Sol and Yona-Kit. But Gray's roots run deep in the punk scene of St. Louis: He toured for years as bassist of the proto-math-rock band Dazzling Killmen, and his most active group in the last decade is the jaw-dropping Grand Ulena. (The free-jazz/noise-rock trio rarely performs live.)

If Darin Gray is one of the area's best-kept secrets, it's a secret he keeps mostly to himself. "There are tons of amazing musicians out there that are terrible fathers and create these broken homes," Kotche says. "But Darin is the opposite. He's a great musician and a great father, and he's definitely an inspiration to me because of that." Gray shares a similar respect for Kotche. "I see Glenn and Jim and many of my other friends succeeding at their art, but these people have made huge sacrifices that maybe I haven't," he says. "It's a shame that artists have to make these sacrifices, because most people don't."

Still, Gray is far from a hermit. In the last few years he's toured Japan five times with Chikamorachi (a trio also comprised of saxophonist Akira Sakata and Björk drummer Chris Corsano) and released an improvisational album, Mimidokodesuka, with Osorezan, his project with Corsano and O'Rourke.

Given Gray and Kotche's individual prolificacy, it seems miraculous that the two were able to find the time to craft Extended Vacation. But incredibly, it's On Fillmore's strongest record to date. Warbling vibraphones and a disjointed bass melody lend an eerie vibe to "Master Moon," while mischievous shakers and percussive toys propel the track into an extraterrestrial climax. Elsewhere, Vacation utilizes hypnotic minimalist repetition, with each interruption coming across like a high-five.

The album's eleven-minute centerpiece, "Daydreaming So Early," sounds like a child feverishly turning the keys of a music box before being distracted by a marching band three blocks away, while the serpentine melodies of "Complications" are juxtaposed with field recordings, as if Kotche and Gray are opening windows to their parallel universe. Subtlety should not be this thrilling.

Kotche is a shockingly proficient drummer (look to "Monkey Chant" from his 2006 solo outing Mobile if you need proof), but the militant snare work of "Daydreaming" is one of the few moments on Vacation when he actually plays drums. Instead, he spends most of his time in On Fillmore behind the vibraphone. "It's really an outlet for us because when we started, I wasn't playing vibes with other people, and Darin wasn't playing upright bass with other people, either," Kotche says. "It definitely brings a balance. It's great to have someone else to work with in a way that's unlike anything else I do."

Adds Gray: "I think the most important thing about On Fillmore, really, is that [even though it's] just Glenn and I, it's a band. After we met, we didn't say, 'Let's play together again sometime,' we said, 'Let's start a band,'" with extra emphasis on the latter word. "My experiences have always been in bands. Even when I play solo, I feel like I'm in a band with myself. I may be grasping at straws, but when On Fillmore uses field recordings, I'm in a band with that recording, or if we work on a movie score, I'm in a band with the movie."

Extended Vacation was released earlier this month on Dead Oceans, the sort of hip record label that young bands dream about. But potential notoriety is not On Fillmore's aim; the sacrifice that Darin Gray and Glenn Kotche make for their art is how infrequently they get to perform it. Extended Vacation is documentation of that which cannot be: a band that barely exists creating places that can only be imagined. But it's not morose, it's not indulgent — and it's most certainly not background music.